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TPS65217 power down after removal of AC input

Toby Prescott
Prodigy 60 points

Hi all,

I am testing the battery backup power switching on a custom board based on the BeagleBone Black RevC board. I have prototypes of my custom board in hand and working relatively well but have run into a problem when trying to test the "fail over" to battery backup if the AC power goes away.

The system runs fine on just AC power or just from the battery. Also charging the battery is working fine. Where I am seeing a problem is when both are connected (AC and Batt) and AC is removed, the UART0 terminal shows:

"Broadcast message from root@beagleboard (Wed Apr 23 20:20:18 2014):

Power button pressed
The system is going down for system halt NOW!"

It then powers down just as if the power button had been pressed. This defeats the purpose of battery backup where we want the system to keep running.

All the power rails measure ok. The power button line does not appear to have any glitches as far as I can see. It does drop from ~5.1V to ~4.1V. I believe this is due to the SYS pins following the change from AC to BATT.

I have tested this on both the BBB RevC and BBB RevA5C which do the same thing!! The kernal is 3.8.13-bone47 and we are running Debian 7.4 

The VERY strange this is that it properly switches from USB power input to Batt without any issues.... 

I am curious if anyone else has seen this issue or has ideas on what could be the going on.

  • 0
    TI__Expert 3740 points
    Toby,

    Based on a hunch that this was something specifically added in and it looks like this patch that is part of the kernel specified (3.8.47) is deliberately shutting off the board when AC power is removed: github.com/.../0001-tps65217-Enable-KEY_POWER-press-on-AC-loss-PWR_BUT.patch

    Have you tried running another Kernel?

    Janice
  • 0 in reply to Janice Escobar
    Prodigy 60 points

    Hi Janice,

    Thanks for the reply. That looks like it is exactly what is happening.

    In my testing since the post, I did try the very latest build from Beaglebone.org and at first thought that it had solved the issue. Then I discovered that sometimes the system boots up and does not correctly initialize somehow. (I'm mostly hardware although on this I have had to get my hands into the software side) When that happens, the power button press is not recognized but I am able to remove the AC power and have the switch-over to battery work as intended. I have also tested with the bare bones SDK image from TI and don't see this issue on that one. So I am leaning very much to a software (feature?) effect.

    It seems to completely defeat the purpose of having battery backup/switchover. I would expect that there should be some user code that would be alerted and can then take some action based on the battery pack size and power strategy.

    It looks like we will have to get out the (software) knife....

    Thanks.